Because of the advantages associated with mobility and ease of deployment, wireless communication systems have emerged as a viable alternative to terrestrial systems. However, because of the high bandwidth requirements of today's applications (e.g., broadband services, digital video broadcast, etc.) along with a continual demand for higher quality of service, the limitations of wireless systems are more pronounced. These shortcomings include limited distance, limited bandwidth, and signal fading, particularly in non-line-of-sight (NLOS) propagation conditions. Under NLOS conditions, severe fading and shadowing problems are present.
To address these concerns, the so-called Multi-Input-Multi-Output (MIMO) systems have emerged to combat fading by providing diversity as well as increased system throughput. For these MIMO systems, multiple transmit and receive antennas are used to support a multiplicity of independently faded paths between transmit to receive antennas, thereby making use of spatial diversity. Spatial diversity improves signal-to-noise ratio in the presence of random fading caused by multipath propagation by combining the outputs of decorrelated antennas.
Conventional MIMO systems target symmetric traffic (peer-to-peer) and moderate quality of service, and thus, are not well suited for wireless applications involving asymmetric communication. One such application is the distribution of audio/video signals within the home. Another drawback with conventional systems is that these systems require complex, costly receivers. The cost of receivers is particularly significant in multiple access systems, thereby hindering widespread deployment. Further, in the context of residential audio/video distribution, the receivers can be moved from room to room; this quasi-stationary environment introduces a challenge in optimizing the MIMO system in terms of diversity and efficient power distribution.
Therefore, there is a need for an approach that effectively supports high data rate, asymmetric wireless applications. There is also a need to utilize inexpensive components, particularly at the receivers.